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Support SIMD on the Emscripten target - #50
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guybedford wants to merge 1 commit into
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guybedford wants to merge 1 commit into
guybedford wants to merge 1 commit into
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Emscripten lowers the SSE2 and SSE4.1 intrinsics to wasm simd128, and cpu.h derives WEBP_HAVE_SSE2/SSE41 from the compiler's __SSE2__ and __SSE4_1__, so passing -msimd128 -msse2 (and -msse4.1 with the sse41 feature) when the Rust target has the simd128 feature is all that is needed. The vendored libwebp still selects its wasm CPU-info path on the legacy EMSCRIPTEN macro that emcc no longer defines; libwebp moved to __EMSCRIPTEN__ in v1.6.0-167 (53394835). Until the submodule is past that, -DEMSCRIPTEN in CFLAGS is additionally needed for the SSE2 paths to be selected at runtime.
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Today
build.rshas no wasm32 arm, so libwebp is built as plain C instead of SIMD there.This adds support for
wasm32-unknown-emscripten, along with the SSE intrinsics flags. Emscripten lowers SSE2 and SSE4.1 intrinsics to wasm simd128 through its emulation headers, andcpu.hderivesWEBP_HAVE_SSE2/WEBP_HAVE_SSE41from the compiler's__SSE2__/__SSE4_1__.Note also that the vendored libwebp still selects its wasm CPU-info path on the legacy
EMSCRIPTENmacro, which emcc no longer defines - libwebp updated use to__EMSCRIPTEN__in v1.6.0-167 (53394835). Until the submodule moves past that commit,-DEMSCRIPTENis needed inCFLAGSadditionally, but I didn't want to hard-code that here since it will be ironed out in the next release and can be set manually in the mean time.All tests are passing on Node.js, to run them, first set env vars:
Then run:
cargo test --target wasm32-unknown-emscripten --no-default-features --features stdIn terms of performance, decoding a 4 MP lossy WebP went from 141 ms (plain C) to about 105 ms with the SSE2 paths active, with identical output.